The invention relates to an improved system for connecting a non-propelled body to a propelled body.
In a typical exemplary embodiment, the invention may be used for connecting trailers to tractors or trucks. In other embodiments it may be used, for example, to connect floating barges to towing craft, gliders or geophysical instruments to tow planes, or suspended loads to helicopters. The invention may also be used where the propelled body pushes the non-propelled body, rather than pulls it.
An important feature of the invention is the creation of a remote force-center forward or rearward of the actual points of attachment to the propelled body.
In the invention, two, three, or four non-parallel and generally convergent links join a propelled or towing vehicle to a non-propelled or towed vehicle, and the links are suitably connected by what may be loosely termed "ball joints", "spherical pairs", or "universal connections" to each vehicle. This linkage places the centers of the force vectors leading from the non-propelled vehicle at a remote point in the self-propelled or towing vehicle usually at or near the center of gravity thereof. As a result, improved steering, better stability, enhanced weight distribution, superior traction, and related advantages are obtained. For example, the tendency to jackknife is overcome. Moreover, these advantages can be achieved without incurring cost significantly greater than those of the connecting systems heretofore in use.
Much of the nomenclature and apparatus of the current technology is derived from old forms traceable to horse-drawn sleds, two-wheel carts and four-wheel wagons. Connecting linkages which are presently in use may be categorized by their applications as follows: towing large semi-trailers from a "fifth wheel" pintle and bearing plate; towing small semi-trailers from a ball hitch; towing four-wheel trailers from a ball or pintle hitch connecting with a tongue; towing long loads where ball and pintle hitches are mounted on "stinger" extensions; plow attachment by linkages of several bars operated by hydraulic jacks and cable devices; towed earth-moving road scrapers locked into rigid units for push-loading; single load lines for loads suspended from helicopters; removable floors to enable suspension of helicopter loads from a real point high inside the helicopter; towing gliders and instruments by single line attachment to the towplane; and similar single line attachment for barges connected to tugs. The invention has application in each of these areas as well as in others, through the planned location of a remote center in the propelled or towing body and the use of a variety of combinations of linkage to achieve this remote center. Each of these arrangements will now be briefly discussed with analysis of the current problems in their use.
The "fifth wheel" pintle and bearing plate is employed for connecting large semi-trailers to towing trucks. Mounting is made on the towing rig's frame above and preferably somewhat forward of the center of the rear axle assembly. This arrangement significantly limits the use to which the towing rig may be put, because the large space between the fifth wheel and the rear of the tow rig is no longer available for cargo. Among the disadvantages of this system is a dangerous tendency to "jackknife" when braking under slippery road conditions, because the trailer steering center is at or near the fifth wheel pintle and so is usually aft of the neutral location at the loaded truck's center of gravity. A variety of cable and hydraulic locks and electronic brake-actuating devices are currently being marketed in attempts to relieve the jackknifing problems caused by this unstable towing geometry.
Another problem with fifth wheel towing systems is that on an excessively bumpy road the trailer pintle can oscillate fore and aft due to slack, causing tremendous shock and wear and risking total separation of the trailer from the truck.
Small semi-trailers are usually towed and carried from a ball hitch mounted at the rear of the towing vehicle, thereby preserving passenger and cargo space. Attachment is most commonly made to the frame or directly to the rear axle of the towing vehicle, the ball extending beyond or above its rear bumper. The large rear overhang between the hitch ball and the rear axle results in a disturbance of the weight distribution and stability of the towing vehicle. The trailer weight tends to lift the towing vehicle's front wheels, causing a reduction in steering control. Jackknifing tendencies are increased from this further rearward location of the trailer steering center. Trailer oscillations cause the towing vehicle to yaw and sway, and vice versa. The long rear overhang causes a coupling of the towing vehicle's and the trailer's oscillations, so that when they have nearly equal pendulum periods, a dangerous buildup of oscillations can occur, especially when traveling at higher speeds on a straight road.
Because of this towing overhang, the weight distribution, steering, and stability problems of small semi-trailers connected by a rear-mounted ball hitch are far more severe than those of large semi-trailers connected by a fifth wheel. Consequently, a variety of spring-loaded load-transfer devices have been marketed for restoring weight to the front steering wheels of the towing vehicle and to the rear axle of the trailer by equal and opposite couples applied to both vehicles at the hitch point. Spring and hydraulic frictional damping devices also are available for reducing the swaying of the trailer by restraints on hinge movement that tend to combine the two vehicles more rigidly when traveling on a straight road. These devices, however, do not eliminate the jackknifing and stability problems caused by faulty towing geometry, although their severity is reduced.
Very small one-wheel semi-trailers are usually hinge-hitched to the rear bumper or towing vehicles to provide for up-and-down movements, while restraining the trailing vehicle from turning or twisting. The single trailer-wheel is caster-mounted to permit the wheel to align itself in the direction of travel. The twisting restraints are needed to hold the trailer upright on its single wheel. The turning restraints, however, prevent use in larger, more practical sizes. The long extension from the rear axle to the trailer wheel introduces inertial steering and control moments which, although small because the trailers are small, nevertheless prevent use even in such sizes as a motorcycle trailer. This type of trailer is rare, because its overhung towing geometry prevents its use in larger, practical sizes, and prevents its use with smaller towing vehicles.
Attempts to tow one-wheel and two-wheel semi-trailers by motorcycles have not been practical because of jackknifing force couples during braking and the unstable steering forces which are applied to the rear of the motorcycle through the unfavorable towing geometry.
Full (four-wheel) trailers are commonly towed from a ball or pintle hitch. This connects the rear of the towing vehicle to the tongue of limber of a support-dolly which carries a fifth-wheel mounting from which the rear of the trailer is towed and carried as an ordinary semi-trailer. This "wagon wheel" type steering of the full-trailer requires a long tongue for stability at high towing speeds and a short tongue for tight maneuvering, such as when entering driveways, turning corners, and other maneuvers where only minimal trailer off-tracking is tolerable. These contradictory requirements necessarily result in compromises that are less than satisfactory.
Full-trailers are frequently towed in train behind a semi-trailer, using a short tongue to minimize off-tracking and total train length. A variety of hydraulic, cable, and even permanent locks are being introduced to restrain oscillatory steering movements of these short-tongued wagon-wheel hitches. Such restraint is needed in order to alleviate their dangerous tendency for yawing oscillations. Breakage from high stresses, gross increases of tire wear from side-scrubbing, and loss of ability to enter narrow driveways have been experienced from these attempted solutions which lock the trailer's support-dolly into a rigid or semi-rigid straight-ahead alignment with the towing vehicle to resist the faulty towing geometry.
Ball and pintle hitches are mounted on "stinger" extensions of the frames of logging and pipe-transporting trucks. Similar use is made on parts trains in manufacturing plants. The effect is to reduce or eliminate side-tracking of the trailing vehicle by locating the hitch more nearly midway between the truck and semi-trailer axles. For example, on narrow mountain roads, truck-to-trailer extensions approach a 2:3 ratio, but if high-speed highway travel is involved in the haul, this ratio is considerably reduced. The trailer loads are carried from log and pipe "bunks" mounted on fifth wheel carriers over the truck's rear axle assembly, being distinctly separate from the steering centers at the rear of the stinger extensions. Such specialized arrangements make these trucks unsuitable for carrying other types of cargo.
Pin-jointed plane linkages of several bars, operated by hydraulic jacks and cable devices are in common use for lowering a plow or ripper point, or the cutting edge of an earth scraper or grader blade to its cutting position. Plane "three-point" pin-jointed trapezoidal hitches are common in which the plowing force is exerted from a low point, ahead of the tractor, where the lines of the upper and lower hitch-bar meet at a virtual center. The goal of trying to prevent the plow from overturning the tractor rearwardly by pulling instead from a lower forward point is not completely realized because such plows lack the directional properties needed to hold them at a constant level. Hydraulic cylinders are employed to adjust the diagonal distance across the trapezoid for holding the plow at the constant level. This converts the linkage to a rigid frame which no longer defines the lower draft line that was sought by the designers of these devices.
Earth-moving road scrapers are towed as semi-trailers during hauling, but are locked into rigid units to prevent jackknifing when being loaded with the assistance of a rear-pushing tractor.
A major problem has arisen in the carrying of loads by helicopters. Dangerous instability caused by poorly slung loads has led to sling developments along static, dynamic and aerodynamic principles.
The most dangerous static condition arises when the helicopter attempts to lift a load while not directly vertically over it. The commonly used single lift line fastened to the bottom of the helicopter, or worse, to a rigid subframe below it, pulls sideways on the bottom of the helicopter, tipping the machine away from the load. The harder the machine lifts, the more it tips, until control limits are exceeded, causing an eventual crash if the load is not released in time for the helicopter to recover from its tipped attitude. The tipping is caused by the low mounting point on the helicopter, far below any neutral location high in the machine near its center of gravity.
Another significant problem is dynamic coupling, which arises when the sling's pendulum period is nearly equal to the corresponding pitch-and-roll periods of the helicopter. The low mounting point of the sling, below a neutral location, enhances the load's ability to swing the helicopter and vice versa. Consequently, when the oscillation periods of the helicopter and its slung load are nearly equal, a dangerous buildup of oscillations can occur.
Aerodynamic instability also may occur when a suspended load fishtails to and fro while traveling at higher speeds. Unless the oscillations are reduced, they will induce corresponding oscillations in the helicopter, because of coupling from the low sling-mounted point. Such oscillations are dangerous to stability.
Current practice includes a variety of corrective measures for these sling problems:
a. Special helicopters such as the "Sikorsky Sky Crane" hang the suspended load from a true point, high inside the helicopter. This necessitates major design changes, such as removing the helicopter floor and bottom and relocating its fuel tanks. The method is effective, but drastic. Such redesign is extremely expensive and results in a one-purpose machine that is uneconomical and impractical for carrying passengers and internal cargo.
b. Boeing Vertol developments suspend a single helicopter line coming from a subframe which is attached to the helicopter bottom by four lines. The subframe is narrower than its mounting points to the helicopter; so the directions of the four lines converge to a point beneath the helicopter at the suspended load-lines. When the load-line swings laterally, it pulls the subframe laterally with it in a manner such that the single load-line moves as if it were mounted higher inside the helicopter. The amount of compensating lateral movements depends upon the angularity of the four lines and the vertical location of the coupler point on the swinging subframe where the single load line is attached. Consequently the device must be specially designed for each helicopter on which it is used and cannot function correctly if extra load lines are attached.
c. Dynamic instability is countered by adjusting the sling length to de-tune its pendulum period from that of the helicopter.
d. Aerodynamic oscillations are suppressed by using several attached lines to check the fishtailing. The net effect is to lower the effective mounting point of the sling; therefore, the lines must be skillfully located and slacked to prevent introduction of excessive static instability.
From these developments, existing improved slings can raise the center of oscillation to a more neutral location, or adjust the period by adjusting the load line's length, or reduce aerodynamic oscillation by using extra lines, but cannot do all three of these at once. The user has had to evaluate which of the problems is the most serious, and be content to live with the others.
Attempts to arrange a connecting system in such a manner that a remote steering center is created have been made in the prior art. The problem is, and has been, that they do not really work. A discussion of some of these earlier attempts is nonetheless necessary for a complete understanding of the present invention. Since the invention relates principally to embodiments having two-, three or four-link systems for creating a remote steering axis, the discussion of prior art will be likewise arranged.